1. Field of the Invention
This invention relates generally to adjustment or trimming systems for frequency devices such as oscillators, crystals and surface acoustic wave filters and resonators. Specifically, this invention is a system for trimming devices to a pre-determined frequency by removing intrinsic or previously deposited materials through a controlled plasma ion bombardment process.
2. Description of the Related Art
In the prior art, trimming of frequency devices such as oscillators, crystals and surface acoustic wave filters and resonators depended on several techniques. For those devices where material such as precious and semi-precious metal is deposited or sputtered on to the frequency device, the technique is to carefully control the deposition of material on the frequency device such that the target frequency is achieved without the necessity of the subsequent removal of the deposited material. A disadvantage to this technique is the requirement to constantly attend to the deposition apparatus to insure that an adequate supply of deposition material was available within the apparatus during the deposition process. Another disadvantage to this technique is that the deposition of material take place on a part by part basis, which is a time consuming, and thus costly process. Also, extreme care must be exercised not to over deposit the material on the frequency device.
A second technique relied on batch processing of the material deposition on several devices simultaneously. The batch processing aspect of this technique would require the over approximation of the target frequency by depositing perhaps slightly more material than required. Following the deposition step, each part would be individually trimmed to the target frequency by a plasma ion process or other suitable process to remove a small portion of the deposited material. For those frequency devices not undergoing deposition of material, the trimming of intrinsic material, e.g. material comprising the substrate, such as silicon dioxide, also requires a part by part process under the prior art. Again, the time consuming nature of trimming each part individually, whether trimming of deposited material or intrinsic material, is a disadvantage to this procedure.
Therefore, a solution to the costly and unproductive limitations imposed by the prior art was needed for trimming frequency devices to the target frequency.